Android security system will ask you about "OpenVPN Connect" app attempts to create VPN connection. Turn on "I trust this application" checkbox if you want to rid off this confirmation dialog in future and tap "OK".

Tap "Continue" since Trust.Zone does not use a client certificate.

uk-man.trust.zone [Trust.Zone-United-Kingdom-Manchester]

After VPN connection will be established "key" icon and green OpenVPN icon will appear in the notification area. When you don't need VPN connection anymore you can tap green switch to disconnect.